Dental syringe apparatus are employed by dentists to deliver a stream of pressurized fluid such as water or air to the inside of a dental patient's mouth. Dental syringes are typically connected to pressurized fluid delivery systems and include a handpiece having a trigger mechanism and an elongate nozzle for generating a pressurized fluid stream.
Most dental syringe systems also include draw-back apparatus which produce a partial vacuum in the dental syringe so as to draw fluid located within the syringe back into the delivery system upon release of the trigger mechanism.
While draw-back apparatus prevent the leaking or dripping of liquid from the discharge orifice of a syringe nozzle when the syringe is not in use, they are not without their disadvantages. More specifically, draw-back apparatus may cause a dental patient's blood, saliva and other residual bodily fluids to be sucked into a syringe, especially if the terminal end of the syringe nozzle is in contact with or in close proximity to a work area within the patient's mouth when the trigger mechanism is released. The drawn-in bodily fluids will remain with the syringe until the trigger mechanism is reactivated. Upon reactivation of the trigger mechanism, the drawn-in fluids will be discharged from the syringe, possibly into another patient's mouth, thus causing the transmission of of any contagious diseases carried in the residual bodily fluids of a previous patient to a subsequent patient.
Accordingly, unless precautions are taken, the use of dental syringe systems to dispense fluid streams to work areas within a dental patient's mouth presents a significant risk of residual cross-contamination to dental patients.
In an effort to reduce the health risks associated with the use of dental syringe systems, a variety of dental syringe safety sheaths have been conceived. These dental syringes safety sheaths typically include a disposable resilient tubular member which is configured to cover the nozzle of a dental syringe and an aperture at the terminal end thereof through which a preferred fluid stream may be discharged. Such safety sheaths also commonly include valve means intended to prevent the residual bodily fluids from be drawn back into the sheaths upon termination of the fluid stream to a work area within a patient's mouth.
One type of valve which has been used to prevent the reverse flow of fluids in a wide variety of applications is the duckbill valve. A typical duckbill valve is shown generally at 50 in FIGS. 6, 7 and 8 of U.S. Pat. No. 4,524,805, issued to the above-identified inventor. Valve 50 includes a body member 52 which defines a fluid passageway 54. Body member 52 smoothly tapers from an inlet end 56 to form a wedge edge shaped outlet end 58 having an outlet slit 59 defining a pair of resilient sealing lips 60 and 62 of a uniform width. The cross-section of sealing lips 60 and 62 between the ends of outlet slit 59 is substantially narrow relative to the length of slit 59.
In operation, valve 50 is usually positioned in line with a fluid conducting conduit (not shown). A stream of pressurized fluid is directed along the conduit and into the inlet end 56 of the valve 50 along the fluid passageway 54 to outlet end 58 where the pressure exerted by the fluid flowing between normally closed sealing lips 60 and 62 deforms the lips so as to permit fluid flow therethrough. If fluid flow stops or reverses direction, the resilient lips are intended to have a closing bias such that the lips will resume their normal shape and position in sealing engagement against one another.
Duckbill valves are usually formed of a resilient elastomeric material which is molded into a configuration substantially similar to that shown in FIGS. 6-8 of the U.S. Pat. No. 4,524,805 referenced above. The forming process often results in a slight amount of heat induced shrinkage to the resilient material comprising the valve member 52. Significantly, the amount of lip shrinkage in lengthwise direction is typically greater than the amount of shrinkage in the tranverse direction. In consequence, a slight opening bias is typically imparted along the length of lips 60 and 62. The slight opening bias normally urges the sealing lips into a slightly open position under no flow conditions. Duckbill valves of conventional duckbill type construction thus are commonly susceptible to small amounts of leakage under no flow and low flow conditions.
While small reverse leaks in a duck flow valve may be acceptable in non-dental applications, it is clear that even the most insubstantial reverse leak in a dental syringe poses an unacceptable health risk to dental patients.
Previous attempts at preventing reverse flow leakage in dental syringe sheath apparatus are exemplified by U.S. Pat. Nos. 4,998,880 and 5,197,875, issued to Nerli. The '880 patent teaches the use of a flap-type valve and/or ball-type valve insert, in conjunction with dental syringe safety sheath apparatus, to minimize residual cross-contamination problems. It is believed that the flap-type valve described in the '880 patent is susceptible to reverse flow leakage problems. While the ball-type valve may be effective in preventing reverse flow, the insert adds to the complexity and expense of the safety sheath. The '875 patent teaches the use of a duckbill valve also to minimize residual cross-contamination between dental patients. However, as noted above, duckbill valves typically have a slight opening bias under no flow conditions and thus, like the flap-type valve of the '880 patent, are susceptible to reverse flow leakage problems. In this regard, it is noted that the patentee of the '875 patent retained the assignee of the present application to manufacture a prototype of a dental syringe safety sheath having a conventional duckbill valve at its terminal end. The prototype, manufactured in accordance with the patentee's specifications, included a pair of sealing lips of a rectangular cross-section (between the ends of the slit disposed therebetween) terminating in a pair of lip margins having rounded outer edges. The sealing lips had a combined width of 1.3 millimeters (between the ends of the slit) as compared to a sealing lip length (measured along the slit) of 3.7 millimeters. Tests of the prototype indicated that the valve did not adequately resist reverse flow leakage problems and that, as such, the design was not suitable for use in dental applications.
A low cost duckbill valve which is more resistant to reverse flow leakage is illustrated in FIGS. 1-5 of U.S. Pat. No. 4,524,805 referenced above. The improved duckbill valve 10 described in that patent includes a pair of sealing lips 20 and 22 having enlarged or widened lip margins 24 and 26 adjacent the opposing ends of slit 19 which elastically resist the opening of the lips 20 and 22. While it is believed that a duckbill valve manufactured in accordance with the disclosure of that patent demonstrates improved resistance to reverse leakage problems relative to predecessor designs, valve 10 was not conceived specifically for use in medical-related applications wherein reverse flow leakage poses significant health risks to dental patients. Thus, there remains a need for one-way valve of duckbill type construction which is even more resistant to reverse flow leakage problems and which can be utilized in conjunction with a dental syringe safety sheath apparatus to minimize the risk of residual cross-contamination between dental patients.
Accordingly, it is a principal object of the present invention to provide a dental syringe safety sheath with a modified duckbill valve having a closing bias which is more resistant to reverse flow leakage.
It is also an object of the present invention to provide a dental syringe safety sheath having a modified duckbill valve which can be easily engaged with or disengaged from the nozzle of a dental syringe and which can be disposed of after use with each dental patient.
It is yet a further object of the present invention to provide such a dental syringe safety sheath at a low cost.